The present invention relates to an endoscope and, more particularly, to an endoscope requiring a light source when an object under examination is in shadow or is completely dark.
When a body cavity or a narrow body passage is observed with an endoscope, an object therein is in shadow or is completely dark. A light source for illuminating the object is thus required. There are two types of light sources, i.e., an external light source type wherein the light source is provided outside the endoscope main body, and an internal light source type wherein the light source is incorporated in the distal end of the inserting section of the endoscope.
In the external light source type endoscope, a light source unit is provided outside the endoscope main body. The light emitted from the light source unit is transmitted to the distal end of the inserting section of the endoscope through an optical fiber bundle called a light guide, and irradiates the object through an illumination optical system. However, the illumination light emitted from the light source unit is attenuated during transmission in the light guide. Therefore, the intensity of the illumination light depends on the illuminance of the light source lamp in the light source unit and the light transmissivity of the light guide.
An endoscope is often inserted in a narrow body portion as described above. If the number of the optical fibers is increased to obtain a light guide with a larger diameter, in the interest of improving the light transmissivity of the light guide, the diameter of the inserting section is undesirably increased. For this reason, in order to increase the intensity of the illumination light, a light source lamp with a higher illuminance must be employed in the light source unit. This leads to an increase in the size of the light source lamp. The size of the light source unit itself must be increased to avoid adverse effects caused by heat generation, resulting in high cost.
In the internal light source type endoscope, when the intensity of the illumination light is to be increased, a light source lamp with a higher illuminance must be employed. In other words, a light source lamp of a larger size must be employed. In this case, however, the diameter of the distal end of the inserting section becomes undesirably large. In addition, the distal end of the inserting section becomes hot due to heat generation, endangering the body portion under examination.
For the above reasons, it is difficult to increase the intensity of the illumination light in the conventional endoscope.